The nematode, C. elegans, has been identified as a "high connectivity" animal for cellular development. This very small, simple animal has been widely adopted for experimental study due to its excellent genetics and accessible cell biology. The complete genome of the worm has been published, and most of the adult anatomy has been reconstructed from electron micrographs of serial thin sections. However, EM techniques are not widely utilized by the C. elegans community, and most previous EM data are not easily accessed. The Center for C. elegans Anatomy concentrates on extending the EM methods in C. elegans, particularly to: 1) study cellular changes during normal development and in mutant animals; and 2) conduct EM-immunocytochemical studies to localize antigens at the ultrastructural level. Such studies are being conducted in close collaboration with NIH- and NSF-funded laboratories, in fulfillment of their existing experimental aims. In addition, the Center is: 3) publishing more detailed information regarding the anatomy of the nematode in the form of annotated electron micrographs. The information is available on CD-ROMs, and will soon be on the World Wide Web, and possibly in book form. Where necessary, the Center is: 4) testing new EM methods for the nematode, and conducting additional EM surveys of the wild-type anatomy at several developmental stages to supplement the Atlas, and particularly to fill gaps in our general knowledge. The Center also provides: 5) training in transmission EM methods so that more C. elegans laboratories can conduct their own EM studies. This Pre-Resource (R24) application will continue to build the capabilities of the Center over a five year period; it was formally opened in February 1998.